This invention relates to a wing and trailing edge flap structure for short takeoff and landing (STOL) aircraft, and more particularly, to a trailing edge flap system that creates a smooth downward and rearward extension of the upper airfoil surface upon extension and that, when extended, can be altered in flight to create spanwise aerodynamic slots in the flap system to enhance aerodynamic lift.
Several applications are related to the subject matter disclosed herein. They include Lewis et al, Ser. No. 339,734, filed Mar. 9, 1973, now abandoned and refiled as a continuing, copending application, Ser. No. 520,674, filed Nov. 4, 1974, and Cole et al, Ser. No. 339,645, filed Mar. 9, 1973, now U.S. Pat. No. 3,837,601, all of which are expressly incorporated herein by reference.
The present invention has particular application in STOL aircraft using upper surface blowing. The engines of an aircraft employing upper surface blowing are mounted forwardly and above the wings to discharge their exhaust stream chordwise across the upper airfoil surface of the wing. During normal flight, the exhaust stream is directed rearwardly to generate forward thrust in a conventional manner. Upon landing and takeoff, trailing edge flaps are employed with such aircraft to increase the camber and chord of the wing and at the same time to form a continuously curved, downward and rearward extension of the upper airfoil surface of the wing. When the trailing edge flaps are so extended, the exhaust stream traveling chordwise over the upper airfoil surface of the wing attaches itself by the Coanda effect to the downwardly and rearwardly curved surface to divert the exhaust stream downwardly and rearwardly. In this manner, a lift component, as well as a forward thrust component, is generated by the exhaust stream. The engine-generated lift component augments the conventional aerodynamic lift created by ambient air flow over the remaining portion of the wing to provide a STOL capability.
As disclosed in the aforementioned copending applications, a serious problem is encountered when engine failure occurs during landing or takeoff. When an engine fails, the engine-generated lift is lost, as well as the forward thrust component otherwise derived from the inoperative engine. When this occurs, a substantial portion of the total lift acting on the aircraft is lost, creating an emergency situation. In addition the extended flaps create a substantial amount of drag, further reducing the net forward thrust acting on the aircraft. Flap systems for partially alleviating the emergency situation by restoring some aerodynamic lift are disclosed in the aforementioned applications. These flap systems generally comprise apparatus for rearranging the flap structure to eliminate the smooth, continuous upper airfoil surface, and at the same time, forming spanwise slots in the flap system. These slots allow the extended trailing edge flaps to function as conventional slotted flaps similar to those used on many commercial aircraft today.
The flap systems disclosed in the aforementioned applications solve the problem by arranging the flap segments to normally form a slotted flap configuration when extended. Slot closure devices are then employed to cover the slots and to form a smooth, continuous, downwardly and rearwardly curved, upper airfoil surface. In one embodiment, the slot closure device is added to the flap system by positioning a flexible panel on the leading edge of each of the flap segments. An actuator is mounted on each of the segments to move the flexible panel between a position in which the slot is closed and a position in which the slot is opened. The addition of the slot closure devices makes the flap segment construction more complex and more expensive. In addition multiple actuators are required, not only on each segment, but because of structural limitations in the flexible panel at several locations along the span of the flexible panel.
A broad object of the present invention is to provide a trailing edge flap system that has the capability to normally function, when extended, as a continuous downward and rearward extension of the upper airfoil surface of the wing and, in addition, have the capability to function as a conventional slotted flap should an emergency such as an engine failure occur. More specifically, it is an object of the present invention to provide such a flap system that is less expensive to manufacture and that is less complex and simpler in design than the flap systems disclosed in the aforementioned applications and that requires minimum of operating mechanism to actuate. In this context it is another object of the invention to provide the foregoing attributes in an externally hinged flap system without employing separate slot closure or opening devices.